Refrigeration system



ot.2o,1942. Y R. E. STORK HM,l 2,299,188

REFRIGERATION SYSTEM Filed March 13, 1940 ATTORNEYS Patented Oct. 20, .1942

i orFiCE REFRIGERATION SYSTEM Ralph E. Stork, Hohokus, N. J., and Robert C. Russell, Greene, N. Y.

Application March 13, '1940, Serial No.. 323,716

6 Claims.

This invention relates to refrigeration systems, and particularly to systems which employ a readily liqueable gas such as ammonia as the refrigerant and use the refrigerant when con- In general the capacity of an ammonia refrigeration system is proportional to its back pressure at constant head pressure. In other words, within certain limits and by reason of the greater density of the ammonia taken in on the suction stroke of the compressor, the greater theV back pressure the greater the capacity of the apparatus for the same displacement. As an illustration, an 8x8 compressor operating at 327 R. P. M. will have a capacity of approximately 241/2 tons per twenty-four hours at 10 pounds back pressure and a capacity of tons per twenty-four hours at 20 pounds back pressure.

Furthermore, the horsepower per ton of an ammonia compressor varies with the back pressure and that with an increase in the b ack pressure the horsepower per ton decreases. Using the above conditions as a basis for the computation of the. horsepower per ton, the total horsepower used in producing 241/2 tons at 10 pounds v back pressure would be 47, while the total horsepower used in producing 351,4, tons at 20 pounds back pressure would be 53.75. This gives an increase in capacity of the same compressor of 43.8% with an increase in power consumption of only 14.3%. Reduced to horsepower per ton, this means that the horsepower per ton at 10 pounds back pressure is 1.93, while at 20 pounds back pressure it is -only 1.525, or a saving in power per ton of .405 horsepower or 21%.

The present invention aims particularly so to construct and arrange ammonia or other refrigeration systems, in which brine or other suitable liquid is employed as a heat transfer and refrigeration storage medium, that full advantage may be taken of the thermodynamic relations above set forth.

It has been standard practice, in the design of ammonia refrigeration systems utilizing brine as a heat transfer, heat conveying and refrigeration storage medium., to employ a pump to take the brine from the brine tank, in which it may be at a temperature of anywhere from 0 up to 25 F.,

and first force the brine through a brine cooler, where it is in heat exchanging relation to the liquid ammonia and in which its temperature is lowered still further, and then through the cooling or heat transfer equipment, where it is in heat exchanging relation to whatever is to be refrigerated, and finally b-ack to the brine tank. Depending uponthe temperature of the brine as it is taken from the brine tank and forced through the brine cooler, the amount of heat given up to the liquid ammonia in the brine cooler will vary, but in vgeneral it will not be suicient to cause a very high back pressure on the ammonia compressor.

One of the objects of the present invention, therefore, is so to construct and arrange an ammonia refrigeration apparatus that, while the reserve refrigeration capacity and the adaptability to meet a wide range of load conditions which are provided by the use of a brine storage tank may be available, at the same time the brine will be so circulated through the system as to insure both full use of its heat exchanging lcapacity and a higher average back pressure on the compressor and thus a higher operating efficiency of the compressor. To this end an important feature of the invention is the employment of two circulating pumps, preferably operating at constant speed', one for effecting the movement of the brine from the brine tank through the cooling or heat exchange equipment, and the other for effecting `the movement of the brine from what may be, forv convenience, termed a hot well through the brine cooler. Another important feature of the invention is the provision of the hot well itself.

Another object of/the invention is so to arrange the circulation effected by the two pumps aforementioned that, vvhile provision is made for operating both at full capacity and provision is also made for insuring a higher average back pressure on the compressor than in the refrigeration storage systems of the prior art, nevertheless the desired refrigerating conditions can be maintained for whatever is to be refrigerated.

Other objects and important features of the invention will appear from the following description and claims when considered in connection with the accompanying drawing, in which A Figure 1 illustrates a refrigeration systemembodying the present invention, some of the partsl upper part of a float-controlled accumulator 4 through a suction line 6 and on its compression stroke forces the ammonia gas or vapor through the pressure line 8 and through an oil drip or separator l into the condenser I2, which may be of the shell type, where the compressed ammonia vapor is brought into heat exchanging relation to water circulating from any suitable source of Water supply such, for example, as anA inlet I4 from a water main and an `out1et I6 to the plant line. The condensed ammonia is discharged from the condenser I2 into a storage reservoir I8 from which it may pass through a communicating pipe 20 to the accumulator 4 having a float level control 22, which operates, Whenever the level in the accumulator falls below a predetermined point, to open connections to the reservoir I8 to restore the level.

From the accumulator 4 the liquid ammonia passes through the down pipe 24 to the brine cooler 26, which may also be of the shell type and in which the liquid ammonia is brought into heatexchanging relation to the brine to be cooled, the mixture of liquid ammonia and ammonia vapor or gas then returning to the accumulator 4 through the up pipe 28 from which it isv discharged into the top of the accumulator 4, the liquid dropping into and mixing with the mass of liquid in the accumulator 4 and the ammonia gas or vapor remaining above the surface of the liquid in position to be drawn into the suction pipe 6 on the suction stroke of the compressor 2.

From the foregoing description it will be seen that the higher the operating temperature level in thel brine cooler 26 the greater will be the' pressure on the ammonia gas or vapor above the liquid level in the accumulator 4 and thus the greater the back pressure on the compressor 2. To insure such high temperature operating level in the brine cooler 26 and thus a back pressure of considerable amount upon the compressor 2, while maintaining the desired refrigerating temperature and operating the circulating mechanism at its full capacity, is one of the objects of the present invention.

The brine for cooling the refrigerator 38 is taken from a brine tank 32 by a pump 34 Which forces it through the refrigerator 38, the brine entering the refrigerator 30 through the pipe 36 which branches to the several coils of the refrigerator. From the refrigerator coils other branch pipes conduct the brine to a return pipe 38 which connects both with a pipe 40 leading to the hot well. hereinafter to be described, and with a pipe 42 which may be used when desirable to re-introduce a part of the heated brine into the intake 44 leading from the brine tank 32 to the pump 34. Whether or not any of the heated brine is to be mixed with the brine going from the brine tank 32 to the pump 34 is determined by the temperature of the brine in the pipe 36 and '"by the desired refrigerating temperature. A thermostat 46, located in the pipe 36, has a connection 48 to a valve 50 in the pipe 42. If the brine in the pipe 36 be colder than is desirable for the particular refrigerating operation, then the thermostat 46. having been set for the desired operating conditions, opens the valve 58 sufficiently to allow a mixing ofthe heated brine with the brine from the tank 32 in order to bring the temperature of the brine in the pipe 36 to the desired level.

In order to effect a partial separation of the heated brine, coming from the refrigerator, from the colder brine in the tank 32 and at the same 75 time to provide uninterrupted full capacity circulation of brine by the pump 58 through the brine cooler 26, the pipe 46 in Figure 1 of the drawing is led into a compartment 52 separated from the main part of the brine tank 32 by walls 54, this compartment 52 being one form of the so-called hot Well of the present invention and being shown as located in the near left hand corner of the brine tank 32, shown in section in Fig. 1.` From the compartment 52 an intake 56 leads to the additional brine circulating pump 58 which circulates the brineI through the brine cooler 26, the pump. 58 being connected to the cooler 26 by a pipe 60 and the brinedischarged from the cooler 26 being conducted back through a pipe 62 to the main part of the brine tank 32 where it is introduced near the bottom of the tank.

From the foregoing description it will be seen that in some cases all of the brine that is forced through the refrigerator 38 by the pump 34 will not be conducted through the pipe 40 into the hot well 52 but that part of it will be diverted through the branch 42. In order, therefore, not to interfere with the circulation of brine through the brine cooler 26 and to insure full capacity operation of the pump 58, a connection is made between the hot well 52 and the main part of the brine tank 32, such, for example, as an opening or openings 64, to permit colder brine from the tank, sufficient to insure proper supply to the pump 58, to mix with the heated brine which comes from the refrigerating coils of the refrigerator into the hot well 52 through the pipe 48. However, to insure that the heated brine which comes in through the pipe 48 will be drawn into the pump suction, the outlet of the pipe 48 in the hot well 52 is brought down pretty well toward the intake 56. Moreover, the openings 64 should be at a level above the discharge end of the pipe 62 and high enough above the bottom of the tank 32 so that the brine coming into the hot well 52 through them will be from the warmer upper portions of that in the tank. These openings 64 also provide brine for the operation of the pump 58 when the pump 34 is not running,'that is when there is no refrigeraoutside the brine tank 32 but connected thereto-- by a pipe 68 which enters the tank 66 preferably below the upper level of the brine in the tank 32 but above the outlet of the pipe 40, so that the brine drawn from the tank 66 by the pump 58 through the connection 'I8'. will be made up as far as possible of ythe heated brine coming from the refrigerating4 equipment through the pipe 40, when the pump 34 is operating.

From the foregoing description the theory of operation and the economies effected by the improved refrigeration system willfreadily be understood. In a refrigeration system of this general type, that is, one employing a brine tank and a brine cooler, there will, under ordinary conditions of operation, be a definite temperature relation of the ammonia to the average temperature of the brine going into the brine cooler. This relation will change slightly with'4 change in back pressure because of the fact that 'more work is being .done by the system at higher back pressure than at lower back pressure.

However, with constant pump capacity the temperature drop in the brine in passing through a brine cooler, such, for example, as the brine cooler 26 of the shell type hereinabove referred to, will increase slightly with increase in back pressure and decrease slightly with a drop in back pressure. An increase in the temperature of the brine passing through the brine cooler 26 will cause an increase in the ammonia temperature with a corresponding increase in back pressure. Although the temperature of the ammonia will not be directly proportional to the brine temperature throughout a wide temperature range, for the purposes of comparison of the advantages of this invention with prior practice vit will be near enough to say that an increase of 1 in the initial temperature of the brine Will mean an increase of 1 in the temperature of the ammonia multiplied by the rates of capacity at increased back pressures over the initial capacity.

The efficiency of the hot well of the present invention depends to some extent upon lthe relative amounts of brine circulated by the two pumps. For example, if the brine cooler pump 58 has a capacity of twice the pump 34, which circulates the brine through the refrigerating equipment, the increase in the temperature of the brine entering the brine cooler 26 will be less than if the two pumps 54 and 34 were of equal capacity.

In the practice of the present invention the relation of the circulation capacities of the two pumps will vary according to the application, type of load and the relation of the capacity of the actual refrigeration load to the capacity of the machine. As an example, a refrigeration systern embodying the present invention has been installed, in which the ratio of circulation of brine by the brine cooler pump 58 to the circulation by the refrigeration equipment pump 34 -is 1% to 1 in a plant in which the maximum load. is 21/2 times the operating machine capacity, while at another installation embodying the present invention the circulation effected by the pump 34 varies from a relation of 1 to 11/2 in respect to the circulation eiected by the brine cooler pump 58, at one time, to a relation of 1 to 1 at another time.

Experience has also shown that the economies effected by the improved refrigeration system are still more marked the longer the refrigeration load lasts. This is illustrated somewhat in the following table which shows the temperature and pressure characteristics of the improved system in an existing installation:

ordinary brine-tank ammonia refrigeration systempperates without the "hot, Well of the present invention, there being in condition 1 no hot well action. n

The readings for condition 2 show the immediate eiect which the hot well exerts when refrigeration load is applied. The readings under 3 show the eifect after three quarters of an hour of operation with substantially constant application of refrigeration load. The readings under 4 show substantially the average condition of the run, while the readings under 5 show the maximum benefit of the hot well at the end of the run.

It is to be noted that the refrigeration system embodying the present invention from which the above table of readings was made embodied also the automatic brine recirculation control, including the by-pass pipe 42, the thermostat 46 `and the thermostatically controlled valve 50, for maintaining substantially constant refrigeration conditions and 'that only the overflow, that is, that 'part of the heated brine owing through the pipe 38 which was not by-passed again to the pump 34, was carried on through lthe pipe 40 into the hot well. In some systems embodying the present invention the by-pass 42 is not employed and all of the brine from the refrigeration coils is returned to the hot well.

Referring again to the above table and taking the readings under 4 as the average condition, it will be noted that the brine enters the cooler 26 at a temperature of 22, Whereas the temperature of the brine in the tank 32 is 14. This gives an increase of the temperature of the brine entering the cooler 26 by reason of the use of the "hot well over the temperature of the brine, had

' it been taken directly from the brine tank, of

8 F. It will also be noted that with this average condition the back pressure is 22 lbs. gauge and the ammonia temperature '7.9 F.

In order to make comparison with the ordinary brine tank refrigeration system, that is, a brine tank system operating without a hot Well, we may by computation determine the approximate conditions as to ammonia temperature and back pressure in such' a system with the same brine tank temperature. In doing so,l two things must be taken into consideration, namely, first the actual temperature diierence in the ammonia. in

, the two systems and, secondly, the fact that the capacity of the compressor for the same displacement will decrease with a decrease in back pressure.

Taking all of these things into consideration, the actual ammonia temperature for an average brine tank temperature of 14 F. in th'e ordinary Brine v Temperature Temperature tank Back of brine 1n of brme out NHaF Time telgra' shell cooler shell cooler pressure (1) Comressor operating without plant Degrees9 Degree? Degrees 7 Pow/nie4 Dezgrs 6 15 loa (2) At start of receiving 9 17 13 l5 1 6:30 (3) After hr. operation onload 13 21. 5 18 20 6 7:40 (4) When brine tank warmed hall ci total rise 14 22 18 22 7. 9+ 7:50 (5) At insh 19 27 23 24 9 8:50

Referring to the foregoing table, the economies brine tank systems operating on the same refrigeffected by the improved refrigeration system can eration load may be estimated to be approxireadily be perceived. For example, the readings -under condition 1, that is,f;when thecompressor is operating without plant load in a milk-receiving station, before the farmers have started to deliver their milk to the station, shows how an mately-'220 F. This corresponds toa back lpressureof 14 lbs.

The H. P. per ton at 14 lbs. back pressure is 1.75. The H. P, per ton at 22 lbs. back pressure is 1.496. It will thus be seen that for the average condition shown in the table above, that is, the condition showing 22 lbs. back pressure, the ratio of H. P. consumption to th'at of an ordinary brine system having an average back pressure of 14 lbs. will be 1.496/ 1.75=85% The improved refrigeration system of the present invention in the illustrative example will thus show a saving in power of approximately 15%.

From the foregoing table' another economy effected by the system can also be seen. This is the fact that the compressor is put to work immediately. This means fewer hours of operation of the same compressor at thesame speed.

Other indirect savings not included in the 15% H. P. saving referred to above are also eiected, one being the fact that the hot well pump 58 will operate fewer hours. For instance, in the illustrative example given -above it is estimated that, without the hot well, the compressor would have operated at least an additional 11/ hours to take care of the increased amount of CFI work resulting from the increased capacity due to the use of the hot well over the amountof work which would have been done by the standard system.

Further to illustrate this point, if an ammonia compressor operating at constant speed has a capacity of tons at 15 lbs. back pressure, th'is same machine, operating .at 22 lbs. back pressure,

will have a. capacity of 24.7 tons. Assuming, then, a total load of 158 ton hrs., the time of operation would be 158/20 or 7.9 hrs. at 15 lbs.

back pressure and 20 ton rate. The time of operation of the same machine, with a 24.7 ton rate at 22 lbs. back pressure, would be 15S/24.7 or 6.4 hrs. The diierence in the operating time would, therefore, be 7.9 hrs-6.4 hrs., or 1.5 hrs,

Another indirect saving is effected by the use of two pumps. In brine tank refrigeration systems such as used in milk-receiving plants of usual capacity and employing only one pump, a

15 H. P. motor is utilized to operate the pump and this motor is operated throughout the entire operation of the compressor which, as just stated, would be approximately 11/2 hours more than with' the hot well system. Although, with the two pumps of the refrigeration system of the present invention, the same total H. P. would be required, it would be distributed as follows:

10 H. P. on the pump 34 which circulates th'e brine through the refrigerator coils, and

5 H. P. on the pump 58 which circulates the brine through the brine cooler.

As sh'own by the table given above, the refrigeration load lasts only about 21A; hours and thus the pump 34 would be driven by its 10 H. P. motor for only 21/2 hours. The pump 58, however, which circulates the brine through the brine cooler 28 operates necessarily for the same period of time as th'e compressor, which is from 5 to 8 hours on the average. This means a saving in power applied to brine circulation of from 21/2 to 51/2 hours on a 10 H. P. motor.

Still another indirect saving comes from the increased capacity of the compressor at the higher back pressure whereby less refrigeration storage or total advance cooling of the brine in the brine tank is required. With the smaller refrigeration storage the nal brine temperature in the brine tank will be higher for the same amount of refrigeration load and will therefore create a higher nal back pressure.' In other words, the machine will have a tendency to keep out of th'e low back pressure or less economical operating range. l

Although in the preferred embodiment of the invention the hot well effect is produced by providing either a compartment in the main brine tank or a separate container for the hot brine, it will be understood that an approximation to the same result may be obtained by omitting the partition 54 and carrying the outlet of th'e pipe 40 down even closer to the intake to the pipe 55 leading to the pump 58, thus insuring that at least a substantial portion of the brine withdrawn from the tank 32 by the pump 58 will be the hot brine introduced through th'e pipe 40. Such an arrangement is intended to be included also' in the expression hot well and, in one embodiment, is shown in Figure 3, where the intake to the pump 58 is shown as provided with a bell mouth 12 into which the disch'arge end of the pipe 40 projects. This provides both for proper direction of the hot brine into the pump intake and also for the entrance of make-up brine from the tank 32 to supply any deficiency, particularly when a part of the hot brine is being by-passed back through the refrigeration equipment. In some casesthe bell mouth 'I2 may not be necessary to secure the desired direction of the hot brine to the pump intake.

It is to be noted that the recirculation of thermostatically selected proportions of the partially heated brine, for controlling the temperature of the refrigerating equipment, is effected in the illustrative embodiment of the present invention by the same pump that forces the brine through the refrigerating equipment, this being one of the novel features of the present invention. In order to insure the desired operation under certain pressure conditions, as, for example, when starting with very cold brine, so that substantially all of the h'eated brine is recirculated, a check valve 45, opening in the direction of flow from the tank 32 to the pump 34, may be sov located in the pipe 44, between the junction of the by-pass 42 with the pipe 44 and the tank 32, as to prevent any tendency ofa rise in pressure of the brine in the by-pass 42 to drive a part of this heated'brine back into the tank 32. The desired pressure relations may obviously also be obtained and maintained in other ways well known to the art.

What is claimed as new is:

1. vIn a liquefied gas refrigerating system, the combination with a storage tank for a heat transfer and refrigeration storage medium, a cooler for said medium in which it is brought into heatexchanging relation to a liquefied refrigerant and then discharged into said tank, a compressor and a condenser for the vaporized refrigerant-from said cooler, refrigerating equipment in which said medium is brought into heat-exchanging relation to whatever is to be refrigerated and a pump for effecting movement of said medium through said refrigerating equipment. of a container -for receiving the medium after it is discharged from said refrigerating equipment, a second pump between said container and said cooler for effecting circulation of the medium from said container through said cooler and back to said tank, means for by-passing a portion ofl the medium, after it 4has passed through the refrigerating equipment,

ldirectly into the intake of the first-mentioned 2. In a liqueiied gas refrigerating system, the

combination with-a storage tankfor a heat trans-m fer and refrigeration storage medium, a cooler for said medium having connections to said -tank whereby the medium may be brought into heatexchanging relation to a liquefied gas refrigerant in said cooler and then discharged into said tank, a compressor and a condenser for the vapcrized refrigerant from said cooler, and refrigerating equipment connected to said tank, of a pump in said refrigerating equipment connections for eiecti'ng circulation of said medium through said refrigerating equipment from the tank, means for varying the amount of said medium withdrawn from said tank by said pump and correspondingly the amount to be discharged from the refrigerating equipment into the tank in accordance with the temperature requirements of said refrigerating equipment, a second pump in the connections between-said tank and said cooler constructed and arranged to produce a substantially constant ow of medium through said cooler and back to said tank, and means for substantially immediately directing'the heated medium discharged from said refrigerating equipment into the intake of said second pump.

3. A refrigerating system according to claim 2 in which the directing means comprises a container having a make-up connection with the tank.

4.A refrigerating system according to claim 2 in which said means for varying the amount of medium withdrawn from the tank comprises a by-pass running from the discharge end of the refrigeratingAequipment to theintake of the rst' tem having therein a storage tank for a heat transfer and refrigeration storage medium, a Y

compressor for a liqueable gas and a heat exchanger through which said medium and said liqueiied gas circulate in heat-exchanging relationto each other, said process consisting in eiecting a substantially uniform flow of said4 l medium through refrigerating equipment, re-

introducing into that part of-l the stream of medium which ows from the tank to the refrigerating equipment a sufficient quantity of the heated 

